1. Field of the Invention
The present invention relates to a vent structure for venting the interior of an extruder barrel to permit the escape of gasses from within the barrel. More particularly, the present invention relates to an extruder vent stack that is so configured as to minimize the passage of plasticated material into the vent passageway, and thereby avoid blockage of the vent.
2. Description of the Related Art
The notion of providing a vent opening in an extruder barrel to permit the escape of gasses generated or liberated during plastication of polymeric materials is broadly known. For example, in U.S. Pat. No. 4,185,060, which issued on Jan. 22, 1980, to Michael Ladney, Jr., a vent arrangement is disclosed in the form of a radially extending vent passageway that provides communication between the interior of an extruder barrel and a vacuum system. However, with vent systems of that type it is possible for the plasticated material to enter the vent passageway, and either to block the passageway, or, alternatively, to be drawn into the vacuum system.
One structural arrangement intended to avoid the problem of plasticated material entering and blocking a vent passageway is shown in U.S. Pat. No. 4,824,448, which issued on Apr. 25, 1989, to Masao Moriyama. The device disclosed in that patent is a generally conical rotor that includes volute-shaped protrusions, and which is rotated in order to mechanically push the plasticated material back toward the screw and thereby prevent it from passing into the vent passageway. That patent also discloses the prior use of a pair of interengaged screws that are carried in a barrel that extends upwardly from the extruder barrel, and that is operated so that the rotation of the screws pushes back the plasticated material to prevent its entry into the gas exhaust pipe.
It is an object of the present invention to provide a vent opening structure which simultaneously permits the passage therethrough of gasses and other volatiles, but that also is so configured that plasticated material is not drawn into the vent passageway.
It is another object of the present invention to provide an extruder vent arrangement in which mechanical pushing or pressing elements are not necessary.